In the manufacture of many ceramic products, a ceramic powder is combined with a binder and a carrier medium such as a solvent, and the combination is formed into a green ceramic tape. The green ceramic tape may be subjected to processing steps such as cutting, lamination, hole punching, and metallization. After such processing steps (if any), the tape or tape laminate is fired to produce a sintered ceramic body.
While green ceramic tapes can be formed by several techniques, the most widely used technique is tape casting. In tape casting, a ceramic powder/binder/carrier medium formulation is cast onto a backing sheet. The sheet, with the green ceramic formulation on its surface, is then passed under a device such as a "doctor" blade which regulates the thickness of the ceramic tape.
In order for the green ceramic formulation to be workable during the tape casting process, a solvent is typically added to the formulation as the carrier medium. For most binders, an organic solvent is used. In recent years, however, the use of organic solvents has become less desirable due to environmental problems associated with their later removal from the tape.
Some binder systems which use water as the solvent or carrier medium have been developed. Examples of some aqueous systems are shown in U.S. Pat. No. 5,086,093. These binder systems are often expensive and require a relatively high proportion of binder compared to the amount of ceramic powder in the formulation. The higher amount of binder results in a lower density green tape which requires more severe firing conditions to densify and which undergoes a greater amount of shrinkage on densification. Many aqueous systems also require lengthy times for drying the tape. These disadvantages have discouraged the adoption of such water-based systems for tape casting.